This invention relates to the field of lighting, and more specifically to a method and apparatus of controlling and powering a solid-state light source such as a light-emitting diode or LED, for a portable battery-powered flashlight.
There is a widespread need for hand-held flashlights and lanterns. One common flashlight includes a two-cell battery for power, an incandescent lamp to emit light, and a simple single-pole switch to connect and disconnect the battery to the lamp. Other flashlights use other numbers of battery cells in order to provide a voltage suitable for various particular conditions. Lanterns often use a fluorescent tube to emit light. Certain keychain fobs use a pair of hearing-aid cells and a red-light light-emitting diode (LED) in order to provide short-range lighting such as might be needed to find a keyhole in the dark.
Battery technology is such that as electrical power is withdrawn from a battery cell, the voltage available across a given current load will decrease. This decreased available voltage across the given load causes reduced light output, gradually dimming the light as the battery charge depletes.
Further, LEDs have voltage, current, and power parameters that must be controlled in order to maximize device life. Commonly, a current-limiting resistor is placed in series with an LED in order that only a portion of the voltage drop from the battery is across the LED and the rest of the voltage drop is across the resistor. This voltage drop and corresponding power loss in the resistor is dissipated as waste heat, which is inefficient for a flashlight which should be designed to emit light.
In addition, it is awkward or difficult to determine the amount of remaining charge in a battery cell, generally requiring removal of the battery from the flashlight in order to measure the remaining charge. In addition, the cost of a separate measurement device can be a negative for this market. Some battery cells today include a built-in liquid-crystal indicator for the charge in the cell, but such a solution requires a separate measurement device/indicator for each battery, and requires removal of the battery from the flashlight in order to perform the measurement and observe the indication of remaining power.
The present invention provides a method and apparatus for an L.E.D. flashlight or other LED illumination source. In one embodiment, a flashlight is described. The flashlight includes a flashlight housing suitable for receiving therein and/or mounting thereon at least one DC voltage source such as a battery. The flashlight also includes a light-emitting diode (LED) housing connected to the flashlight housing, the LED housing including a first plurality of LED units- that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis, the first plurality of LED units including at least seven individual LED units. The flashlight also includes a first electrical circuit that selectively applies power from the DC voltage source to the LED units, wherein the flashlight is of such compact size and low weight as to be suitable for single-handed portable operation by a user, the flashlight further having a purpose of providing general-purpose illumination.
In one embodiment, the LED optical axes of the first plurality of LED units in the flashlight are substantially parallel to one another. In one such embodiment, the flashlight further includes a second plurality of LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis, wherein the LED optical axes of the second plurality of LED units converge or diverge from one another forwardly from the housing.
In another embodiment, an optical spread angle of the first plurality of LED units in the flashlight are substantially equal to one another. In one such embodiment, the flashlight further includes a second plurality of LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis, wherein an optical spread angle of the second plurality of LED units are substantially equal to one another, and different than the optical spread angle of the first plurality of LED units.
In yet another embodiment, the LED units are connected in a parallel-series configuration with at least two LED units coupled in parallel to one another and in series with at least one other LED unit, and the DC voltage source includes at least three battery cells connected in series.
In still another embodiment, the first electrical circuit further includes a control circuit for maintaining a predetermined light output level of the LED units as a charge on the battery cell varies. In one such embodiment, the control circuit maintains an average predetermined light output level of the LED units as the charge on the battery cell varies by increasing a pulse width or a pulse frequency as the charge on the battery cell decreases. In another such embodiment, the control circuit maintains an average predetermined light output level of the LED units by measuring a battery voltage and adjusting a pulse width or a pulse frequency or both to maintain the average light output at the predetermined level. In still another such embodiment, the control circuit maintains an average predetermined light output level of the LED units by measuring an average light output and adjusting a pulse width or a pulse frequency or both to maintain the measured average light output at the predetermined level.
Another aspect of the present invention provides a flashlight including: (a) a flashlight housing, the housing being suitable for at least one of receiving therein and mounting thereon at least one DC voltage source that includes at least one battery cell; (b) a light-emitting diode (LED) housing connected to the flashlight housing, the LED housing including one or more first LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis; and (c) a first electrical circuit that selectively applies power from the DC voltage source to the LED units, the first electrical circuit further including a control circuit for maintaining a predetermined light output level of the LED units as a charge on the battery cell varies; wherein the flashlight is of such compact size and low weight as to be suitable for single-handed portable operation by a user, the flashlight further having a purpose of providing general-purpose illumination.
In one such embodiment, the first LED units being a first plurality of LED units, wherein the LED optical axes of the first plurality of LED units are substantially parallel to one another. In another such embodiment, the flashlight-further includes a second plurality of LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis, wherein the LED optical axes of the second plurality of LED units converge or diverge from one another forwardly from the housing.
In another such embodiment, the first LED units are a first plurality of LED units, wherein an optical spread angle of the first plurality of LED units are substantially equal to one another. In yet another such embodiment, the flashlight further includes a second plurality of LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis, wherein an optical spread angle of the second plurality of LED units are substantially equal to one another, and different than the optical spread angle of the first plurality of LED units.
Another aspect of the present invention provides a method of providing general-purpose illumination of such compact size and low weight as to be suitable for single-handed portable operation by a user, including the steps of: (a) providing one or more first LED units that each emit light and have a reflector for collimating the emitted light forwardly therefrom generally along an LED optical axis; (b) selectively applying power from a DC voltage source to the LED units; and (c) maintaining a predetermined light output level of the LED units as a charge on the battery cell varies by controlling the step (b).
In one embodiment, the step of maintaining maintains an average predetermined light output level of the LED units as the charge on the battery cell varies by increasing a pulse energy or a pulse frequency as the charge on the battery cell decreases. In another embodiment, the step of maintaining maintains an average predetermined light output level of the LED units by measuring a battery voltage and adjusting a pulse width or a pulse frequency or both to maintain the average light output at the predetermined level. In still another embodiment, the step of maintaining maintains an average predetermined light output level of the LED units by measuring a light output and adjusting a pulse energy or a pulse frequency or both to maintain an average light output at the predetermined level.
Yet another aspect of the present invention provides an illumination source, that includes (a) a light-emitting diode (LED) housing including one or more LEDs; and (b) a control circuit that selectively applies power from a source of electric power to the LEDs, the control circuit substantially maintaining a light output characteristic of the LEDs as a voltage of the voltage source varies over a range that would otherwise vary the light output characteristic. In one such embodiment, the light output characteristic that is maintained is light output intensity. In another such embodiment, the control circuit maintains the light output intensity of the LED units as the voltage of the DC voltage source varies by increasing a pulse width, a pulse energy, or a pulse frequency as the voltage of the DC voltage source decreases. In another such embodiment, the control circuit maintains an average predetermined light output level of the LED units by measuring a voltage and adjusting a pulse energy or a pulse frequency or both to maintain the average light output at the predetermined level. In yet another such embodiment, the control circuit maintains an average predetermined light output level of the LED units by measuring an average light output and adjusting a pulse width or a pulse frequency or both to maintain the measured average light output at the predetermined level.
Another aspect of the present invention provides a battery-powered portable flashlight (100) including: a casing (110) suitable to hold a battery; one or more light-emitting devices (LEDs) (150) mounted to the casing; a switch (140) mounted to the casing; and a control circuit (130) coupled to the battery, the LEDs, and the switch, wherein the control circuit drives the LEDs with electrical pulses at a frequency high enough that light produced by the LEDs has an appearance to a human user of being continuous rather than pulsed, and wherein the LEDs have proportion of on-time that increases as remaining battery power decreases. One such embodiment further includes a feedback circuit that controls the pulses so that light intensity produced by the LEDs, as perceived by the human user, is substantially constant across a greater range of battery power or voltage than a corresponding range for which light intensity is equally constant without the feedback circuit. In one such embodiment, the feedback circuit measures a light output of the LEDs. Another such embodiment further includes a battery-voltage-measuring circuit coupled to the control circuit.
Yet another aspect of the present invention provides a method for driving battery-powered portable flashlight (100) having a casing (110), a DC power source mounted to the casing, one or more solid-state light-emitting device (LEDs) (150) mounted to the casing, the method including the steps of: receiving input from a user; and based on the received input, generating a series of pulses to drive the LEDs such that the LEDs have proportion of on-time that increases as remaining battery power decreases.
Still another aspect of the present invention provides an illumination source including (a) a light-emitting diode (LED) housing including one or more LEDs; and (b) a control circuit that selectively applies power from a source of electric power to the one or more LEDs, the control circuit maintaining a predetermined light output color spectrum of the one or more LEDs as a voltage of the source of electric power varies. In one such embodiment, the one or more LEDs comprise one or more LEDs having a first characteristic color spectrum output and one or more LEDs having a second characteristic color spectrum output, the first characteristic color spectrum output different from the second characteristic color spectrum output, and the control circuit controls a pulse characteristic in order to control the proportion of light output having the first characteristic color spectrum output to that having the second characteristic color spectrum output. In another such embodiment, the one or more LEDs comprise one or more LEDs having a characteristic color spectrum output that varies based on applied current, and the control circuit controls a pulse current in order to control the characteristic color spectrum output.
Yet another aspect of the present invention provides an illumination source that includes (a) a light-emitting diode (LED) housing including one or more LEDs; and (b) a control circuit that selectively applies power from a source of electric power to the LEDs to adjust a light output color spectrum of the one or more LEDs.